/?  n4-?i 


Issued  .lunr  :.  1909. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

BUREAU  OF  PLANT  INDUSTRY— Circular  No.  31. 
B.  T.  GAL]  "\\  \\    (  biei  oi  Bun 


NOTES  ON  THE  NUMBER  AND  DISTRIBUTION 

OF  NATIVE  LEGUMES  !N  NEBRASKA 

AND  KANSAS. 


JOSEPH  ALLEN  WARREN, 
Assistant  Agriculturist,  Office  of  Farm  Management. 


• 


L-BOT 

jQC  -'EPT. 


[Cir.  31] 
2 


BUREAU  OF  PLAM  INDUSTRY. 


Chief  of  Bureau,  Beverly  T.  Galloway. 
Assistant  Chief  of  Bureau.  Albert  F.  WOODS 
Editor,  J.  E.  Rockwell. 
Chief  Clerk.  James  E.  Jones. 


B    P    1—470. 

NOTES  OX  THE  NUMBER  AND  DISTRIBUTION 

OF  NATIVE  LEGUMES  IN  NEBRASKA 

AND  KANSAS. 


INTRODUCTION. 


Many  hypotheses  have  been  Formed  to  account  for  the  large  stores  of 
nitrogen  in  virgin  soils,  but  none  of  these  have  been  entirely  satisfac- 
tory. It  seems  to  be  a  well-established  fact  that  small  quantities  of 
ammonia  are  collected  from  the  air  by  rain  and  added  to  the  soil;  also. 
that  more  or  less  nitric  acid  is  formed  by  electrical  discharges  and 
added  to  the  supply.  Some  investigators  have  attributed  the  fixation 
t it' nitrogen  entirely  to  the  latter  cause.  Recently  a  number  of  efforts 
have  been  made  to  show  that  nonsymbiotic  or  independent  bacteria  arc 
the  chief  agents  in  fixing  this  element.  While  it  seems  certain  that 
some  nitrogen  is  added  to  the  soil  by  each  of  these  methods,  it  appears 
to  the  writer  that  there  is  not  sufficient  evidence  to  warrant  a  conclu- 
sion that  any  one  of  them  has  been  the  most  important  factor  in  this 
work.  They  do  not  furnish  a  satisfactory  explanation  of  the  presence 
of  such  large  quantities  of  nitrogen  in  the  soil. 

NITROGEN  FIXATION  IN  SOIL  BY  WILD  LEGUMES. 

Several  experimenters  have  suggested  that  wild  legumes  may  have 
played  some  part  in  this  work,  but  they  have  not  generally  been  con- 
sidered as  important  factors.  The  studies  reported  in  this  circular  indi- 
cate that  this  subject  deserves  more  thorough  investigation  than  it  has 
yet  received  and  that  native  legumes  have  been  of  much  more  impor- 
tance in  this  role  than  has  been  thought. 

Several  years  ago  the  writer  raised  the  question  whether  the  native 
legumes  of  the  prairies  were  sufficiently  numerous  to  have  fixed  the 
amount  of  nitrogen  present.  A  search  for  published  data  on  the  sub- 
ject was  made,  but  none  were  found.  Accordingly,  in  the  spring  of 
L908  a  series  of  investigations  was  begun,  a  preliminary  report  of  which 
is  here  given. 

DIFFICULTY   OF   MAKING  INVESTIGATION. 

Many   difficulties   were   experienced    in    collecting   the   desired    data. 
Not  many  tracts  of  virgin  prairie  remain  in  eastern  Nebraska  and  north- 
eastern Kansas,  except  on  land  that  is  too  wet  or  too  rough  or  stony  to 
isily  farmed.     Furthermore,  most  of  the  grass  plots  that  do  remain 
have  been  pastured  so  much  that   tew  legumes    ire  left.     It  was  ther< 

[Clr.81]  3 


4  NATIVE  LEGUMES  OF  NEBRASKA  AND  KANSAS. 

fore  necessary  to  search  out  the  grass  fields  that  had  been  pastured  the 
least  and  which  at  the  same  time  represented  as  nearby  as  possible  the 
average  farm  lands  of  the  region. 

The  next  difficulty  arose  in  the  fact  that  the  growing  season  of  the 
different  species  is  very  different.  Some  species  of  the  genus  Astra- 
galus, for  example,  are  in  fruit  by  May  and  often  dead  before  July. 
Lotus  does  not  come  up  until  late,  and  the  Psoraleas  do  not  all  show 
their  sprouts  until  about  the  middle  or  end  of  May,  and  by  the  first  of 
August  they  begin  to  break  off  just  below  the  surface  of  the  soil  and  to 
blow  away.  Other  species  are  not  readily  recognizable  till  late  in  the 
season.  From  this  it  will  be  seen  that  anyone  making  counts  will  sel- 
dom find  all  the  legumes  at  any  one  time. 

A  third  difficulty  presented  itself  in  the  irregular  distribution  of  the 
plants.  It  was  not  easy  to  find  areas  that  represented  average  con- 
ditions. Not  only  was  there  a  natural  source  of  error  here  but  a  per- 
sonal one  also.  Having  selected  a  piece  of  land  that  fairly  represented 
a  certain  soil  and  slope  it  was  then  necessary  to  select  the  plots  to  be 
counted.  Here  the  personal  equation  appeared.  With  the  amount  of 
time  available  it  was  not  feasible  to  count  large  areas,  so  the  square 
yard  was  selected  as  the  unit.  If  a  patch  contains  showy  legumes  one 
is  almost  sure  to  select  plots  that  either  have  none  of  these  plants  or 
have  an  unusual  number.  To  avoid  this  unintentional  selection  the 
following  methods  were  employed.  With  eyes  closed  the  writer  would 
walk  a  certain  number  of  steps  which  would  take  him  to  a  point  he  knew 
he  had  not  seen.  For  example,  he  determined  to  walk  100  paces  south 
and  take  his  hundredth  heel  mark  as  the  northwest  corner  of  his  first 
square  yard,  or  he  walked  backwards  to  a  point  he  had  not  seen  and 
marked  the  plot  to  be  counted  in  the  same  way.  Either  of  these  methods 
gave  him  square  yards  selected  purely  at  random.  It  was  not  practical 
to  use  the  English  method  of  throwing  a  hoop,  and  even  if  this  could 
have  been  done  it  is  doubtful  if  any  advantage  would  have  been  gained 
thereby. 

With  many  legumes,  especially  Amorpha  (shoe-string),  Kuhnistera 
(prairie  clover),  and  several  of  the  Psoraleas  (in  some  places  called 
wild  alfalfa),  it  is  often  impossible  to  tell  whether  there  is  one  large 
plant  or  several  plants  grouped  together.  In  cases  where  there  was 
much  doubt  the  group  was  always  considered  as  a  single  plant. 

For  the  reason  stated  it  is  plain  that  the  counts  given  in  the  follow- 
ing table  must  be  under  rather  than  over  the  real  number  of  legumes 
present  on  the  plots  counted.  It  should  also  be  noted  that  several  of 
the  counts  were  made  before  the  legumes  had  all  come  up.  It  was 
hoped  that  several  times  as  much  data  could  be  collected  during  the 
year,  but  the  difficulties  mentioned,  together  with  the  fact  that  much 
of  the  season  had  to  be  spent  in  the  semiarid  region,  limited  the  work 
greatly. 

[Cir.  81] 


NATIVE    LEG1  MES    OF    NEBRASKA    AND    KANSAS. 


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6  NATIVE    LEGUMES   OF    NEBRASKA   AND    KANSAS. 

That  part  of  Table  I  referring  to  the  country  east  of  100°  west  longi- 
tude is  believed  to  be  fairly  representative  of  average  conditions.  The 
parts  referring  to  the  high  plains  and  the  sand  hills  are  so  meager  as  to 
be  only  suggestive.  The  counts  made  on  the  high  plains  were  all  at 
the  eastern  border  and  were  either  on  loess  or  at  the  transition  from 
that  to  the  tertiary.  Farther  west  many  observations  were  made,  but 
legumes  are  much  fewer,  and  the  counting  of  much  larger  areas  would 
have  been  necessary  to  get  results  at  all  reliable.  Here,  too,  the  desic- 
cation of  many  plants  in  the  summer  makes  it  very  difficult  to  secure 
accurate  counts. 

LEGUMES  FORM  A  LARGE  PART  OF  OUR  NATIVE  FLORA. 

The  writer  had  long  been  familiar  with  the  flora  of  this  region  but 
was  not  at  all  prepared  for  such  results  as  are  shown  in  the  table. 
After  the  grasses  (including  sedges)  and  possibly  the  composites,  leg- 
umes form  a  larger  part  of  our  flora  than  does  any  other  group  of  plants. 

If  these  figures  are  representative  or  anywhere  near  it,  it  is  evident 
that  our  farm  lands  from  time  immemorial  have  been  growing  a  full 
stand  of  legumes.  Seventeen  plants  to  the  square  yard  are  enough  to 
fill  all  the  soil  with  their  roots.  Most  of  these  plants,  such  as  Amorpha, 
Kuhnistera,  and  Psoralea,  have  enormous  root  systems  (and  these  genera 
represent  the  large  majority  of  the  prairie  legumes).  A  single  plant  is 
often  sufficient  to  fill  the  soil  with  its  roots  for  a  radius  of  several  feet, 
as  any  farmer  who  has  plowed  up  Amorpha  is  ready  to  testify.  The 
smallest  root  systems  are  probably  those  of  Vicia  and  Lotus,  and  yet 
seventeen  of  these  to  the  square  3*ard  would  seem  to  be  sufficient  to 
gather  a  large  supply  of  nitrogen. 

NODULES  ABUNDANT  IN  WILD  LEGUMES. 

Many  examinations  were  made  to  ascertain  the  prevalence  of  nodules 
upon  different  species.  Large  numbers  of  tubercles  were  found  on  every 
species  examined  and  on  nearly  every  individual,  except  mature  Kuh- 
nistera. Nodules  are  especially  plentiful  on  Psoralea,  Astragalus,  Acuan, 
Meibomia,  and  Lotus.  On  Lotus  the  nodules  are  often  almost  massed 
together  on  the  taproot.  Some  difficulty  was  experienced  at  first  in 
finding  tubercles  on  Kuhnistera,  but  they  are  always  in  evidence  on 
seedlings.  On  the  old  plants  there  is  doubt  whether  typical  nodules 
are  produced  or  whether  the  bacteria  are  in  the  small,  thickened  roots 
which  occur  in  extraordinary  numbers,  almost  in  fasicles,  especially  on 
roots  of  the  previous  year's  growth.  During  the  coming  season  an 
effort  will  be  made  to  determine  this  point.  The  efficiency  of  these 
legumes  as  nitrogen  gatherers  does  not  seem  open  to  question,  however, 
if  the  universal  inoculation  of  the  seedling  plants  is  considered. 

[Cir.  31] 


NATIVE    LEGUMES   OF    NEBRASKA  AND    KANSAS. 
FACTORS  INFLUENCING  THE    DISTRIBUTION  OF  WILD  LEGUMES. 

The  distribution  and  abundance  of  legumes  are  iniluenced  by  many 
factors,  one  of  the  most  marked  of  which  is  the  adaptability  of  the 
locality  for  the  production  of  heavy  crops  of  grass.  Few  legumes  can 
compete  with  a  thrifty  growth  of  grass.  Where  Andropogon  inventus 
(bluestem)  luxuriates,  few  legumes  except  Psoralea  seem  to  be  able  to 
persist. 

On  the  densest  swards  of  BuVbilis  dactyloides  (buffalo  grass),  Vicia, 
Psoralea,  Lotus,  and  Astragalus  are  occasional  habitants,  but  none  of 
them  are  able  to  constitute  a  very  large  proportion  of  the  plant  growth. 
On  poor  soils  and  slopes  where  the  grass  is  thin,  both  the  number  of 
individuals  and  the  number  of  species  of  leguminous  plants  are  usually 
greater  than  on  rich  soils  and  level  tracts,  and  legumes  consequently  form 
a  very  much  larger  proportion  of  the  flora.  But  on  all  soils  and  in  all 
climates  of  the  region,  legumes  peculiarly  adapted  to  the  conditions  are 
present  in  large  numbers. 

In  many  of  the  meadows  in  the  river  valleys  of  Iowa,  South  Dakota, 
and  northeastern  Nebraska,  Crotolaria  sagittalis  covers  most  of  the 
ground.  On  level  sand  beds  near  streams  Acuan  grows  in  profusion, 
and  on  thinly  grassed  sandy  bottoms  Cassia  chamaecrista  (partridge 
pea)  is  often  abundant.  On  many  low  sand  hills  Psoralea  is  almost 
the  only  habitant,  while  on  the  tops  of  sand  hills  where  there  is  little 
vegetation  Phaca  longifolia  is  preparing  the  way  for  more  plant  growth, 
and  is  often  assisted  in  this  work  by  Kuhnistera  villosa  and  several 
other  species. 

LEGUMES  ARE  CROWDED  OUT  ON   THE  RICHEST  SOILS. 

It  does  not  seem  that  most  of  these  legumes  choose  the  poorer  soils, 
for.  in  fact,  many  of  them  grow  much  better  on  rich  soil,  but  when  the 
soil  becomes  rich  in  nitrogen  and  humus  other  plants  which  do  not 
thrive  on  poor  soil  are  able  to  crowd  out  the  legumes.  There  is  good 
reason  to  believe  that  lands  thai  are  now  richest  formerly  supported  the 
densest  leguminous  growths,  except,  perhaps,  where  the  fertility  has 
been  washed  down  from  higher  levels. 

NUMBER  OF  GENERA   AND   SPECIES  IN   DIFFERENT  LOCALITIES. 

While  the  number  and  distribution  of  individuals  on  arable  lands, 
and  not  the  number  and  distribution  of  genera  and  species  in  the  State, 
is  the  important  factor  for  our  purpose,  yet  this  latter  question  deserves 
mention.  Pound  and  Clements'  give  23  genera  and  103  specii 
legumes  as  occurring  in  Nebraska.  There  are  23  of  the  species  charac- 
terized as  inhabitants  of  low  prairies  and  meadows,  which  constitute 
most  of  the  farm  land-.  36  of  high  prairies,  sandy  bluffs,  and  -and  bills, 

"  Pbytogeography  of  Nebraska,  p.  240. 

[Cir.  31] 


O  NATIVE    LEGUMES   OF   NEBRASKA  AND    KANSAS. 

and  16  of  western  table-lands  and  foothills.  Only  a  few  of  these  are 
abundant  and  widely  distributed. 

Of  the  1,022  plants  included  in  the  table  of  legumes  east  of  100°,  340 
are  Kuhnistera,  333  Psoralea,  185  Amorpha,  77  Vicia,  67  Lotus,  12 
Astragalus,  4  Lespedeza,  3  Aragallus,  and  1  Baptisia. 

With  the  possible  exception  of  Astragalus,  Psoralea  is  the  most 
widely  and  evenly  distributed  genus  in  the  State  and  has  probably  been 
the  most  effective  in  fertilizing  the  soils,  closely  followed  by  Kuhnis- 
tera and  Amorpha,  while  Astragalus  has  been  an  important  factor  in  all 
localities.  Astragalus  crassicarpus  (ground  plum)  was  formerly  so 
abundant  as  to  tinge  whole  prairies  with  the  color  of  its  flowers,  but  is 
now  almost  extinct  in  many  sections.  In  much  of  the  western  half  of 
the  region  Lotus  has  been  very  important. 

VALUE  OF   LEGUMES  IN  PASTURES. 

The  value  of  the  native  legumes  lies  not  alone  in  their  ability  to  store 
nitrogen  in  the  soil,  but  in  their  feed  value  also.  Live  stock  always  do 
better  in  new  pastures  than  in  old  ones  unless  tame  grasses  have  come 
in.  It  seems  fair  to  assume  that  this  difference  is  partly  due  to  the 
greater  portion  of  leguminous  forage  plants  in  the  new  pasture,  giving 
a  better  balanced  ration. 

Many  of  the  legumes  are  so  ravenously  eaten  by  stock  as  to  be  exter- 
minated in  a  short  time.  Astragalus  crassicarpus  is  one  of  the  first  to 
disappear.  Cattle  do  not  seem  to  relish  Psoralea  and  Kuhnistera  in 
new  pastures,  but  after  the  more  palatable  legumes  are  gone  these,  too, 
are  eaten  and  disappear,  although  their  vigorous  root  systems  enable 
them  to  endure  a  long  time.  So  far  as  the  writer  is  aware,  Baptisia 
bracteata  (false  indigo,  lead  plant)  is  the  only  native  legume  that  is 
able  to  maintain  itself  in  pastures.  This  does  not  seem  to  be  eaten  by 
stock,  for  it  thrives  in  pastures  even  where  feed  is  scarce. 

LESSON  OF  THE  PRAIRIE  LEGUME  FOR  THE  FARMER. 

Western  farmers  have  been  slow  to  learn  their  lesson  from  nature. 
Nature  on  her  farm  has  kept  up  the  production  of  grasses  and  other 
nitrogen  robbers  by  the  constant  growth  of  legumes.  If  this  fact  had 
been  recognized  sooner  perhaps  there  would  not  have  been  such  reck- 
less exploitation  of  the  rich  soils  of  the  Mississippi  Basin.  For  forty 
years  farmers  have  lost  sight  of  this  and  have  taken  off  grain  crops  (all 
grasses)  continuously  and  doubted  if  this  practice  would  ever  exhaust 
their  soils,  because  they  were  still  productive  after  the  removal  of 
twenty,  thirty,  or  forty  crops.  But  now  the  effect  is  evident ;  farmers 
must  learn  from  the  prairies  around  them  one  of  the  first  principles  of 
permanent  agriculture  and  introduce  leguminous  crops  into  the  farm 
rotation. 

[Cir.  31] 


NATIVE    l.l.'.l  MES   OF    NEBRASKA  .\NI>    KANSAS.  •' 

WILD   LEGUMES  IN  THE  EASTERN   UNITED  STATES. 

After  this  paper  was  prepared  the  writer's  attention  was  called  tn 
Bulletin  No.  100  of  the  Maryland  Agricultural  Experiment  Station,  the 

pertinent  party  of  which  are  quoted  below.  It  was  a  surprise  to  find 
such  close  agreement  between  observations  made  in  two  States  where 
conditions  are  so  different. 

The  wild  plants  of  this  kind  (legumes),  next  to  grasses  and  composites,  form 
a  larger  part  of  our  native  flora  than  any  other  family  of  plants, 
protein  content  is  usually  high  and  they  also  thm   make  most  useful  feeding 
stuffs.     (P.  97.) 

Practically  all  of  the  wild  Maryland  species  examined  have  tubercles  on  the 
roots.       P.  100. 

But  when  we  consider  the  large  areas  of  uncultivated  land  in  Maryland  where 
no  crop  is  or  will  be  grown  under  present  conditions,  the  value  of  wild  legumes 
in  building  up  such  land  by  adding  humus  and  nitrogen  becomes  much  more 
worthy  of  consideration,  especially  if  we  remember  the  fact  that  most  of  our 
waste  woodland  and  tields  are  covered  with  a  natural  growth  of  leguminous 
plants  doing  their  work  without  a  particle  of  labor  <m  the  part  of  the  owner. 
On  many  thousand  acres  of  waste  land  over  one-half  of  the  weed  growth  is 
composed  of  nitrogen-gathering  leguminous  plants.    *  A  great  many  of 

these  species  grow  with  the  greatest  ease  on  dry,  sandy,  or  sterile  land  where 
other  plants  would  not  succeed  until  legumes  had  opened  the  way.     (P.  100. 

Legumes  of  some  kind  are  in  every  climate  and  soil.  In  many  parts  of  Mary- 
land legumes  form  one-fourth  to  three-fourths  of  the  wild  plants.      (P.  106.  i 

Approved : 

James  Wilson, 

Secretary  of  Agriculture. 

Washington,  D.  C,  April  23,  1909. 

[Clr.    i 

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